<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>center-3</title>
    <style>
        .one{
            width:100px;
            height:100px;
            background: red;
            position: absolute;
            top:0;
            left:0;
            right:0;
            bottom: 0;
            margin:auto;
        }
    </style>
</head>
<body>
    <div class="one"></div>
</body>
</html>
